1. Field of the Invention
The present invention relates to a machining center having a number of machine tools which each have a working space for machining workpieces, a clamping station in which workpieces to be machined are clamped into workpiece holders, and a loading device which transports the workpiece holders between the clamping station and the working space of at least one machine tool.
2. Related Prior Art
A machining center of this kind is known from DE 195 16 849 A1. In the known machining center, a number of machine tools are arranged next to one another, a loading/unloading station in which a clamping station is located being provided next to that row of machine tools. In the clamping station, workpieces are inserted into workpiece holders which are held by a pivot arm of a loading device.
After the workpiece holder has been loaded with a new workpiece, the pivot arm is pivoted in and the loading device travels to one of the machine tools, where the pivot arm pivots back out and the workpiece holder is clamped in a fixture holder which is provided in the working space of that machine tool. After machining of the workpiece, the workpiece holder is transported either to another machine tool for a further machining operation or back to the loading/unloading station where the machined workpiece is replaced with a workpiece that is yet to be machined.
The pivot arm of the loading device grasps the workpiece holder on one side, the latter in turn grasping the workpiece to be machined on one side. The fixture holder in the working spaces also grasps the workpiece holder on one side; a buttress can selectably be provided so that clamped workpieces can be better centered.
It has been found that with the known machining center, the handling of the workpieces and workpiece holders is disadvantageous particularly when bulky and/or heavy workpieces are to be machined. On the one hand, surprisingly, the machining accuracy and the reproducibility of the machining operation decrease when heavier and/or more bulky workpieces are used. These disadvantages can be partially eliminated or at least diminished by performing workpiece handling in general at lower velocities. This means, however, that in order to achieve high machining accuracy and reproducibility in the machining of heavy and/or bulky workpieces, the work-piece-to-workpiece time is reduced with the known machining center, which of course is disadvantageous.